Non-diffusing polymeric reducing agents for photographic color emulsions



NGN-DIFFUSENG POLYMERIC REDUCING AGENTS FOR PHOTUGRAPHIC COLOR EMULSIONS Louis M. Minsk and William O. Kenyon, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey No Drawing. Application April 15, 1952, Serial No. 282,490

17 Claims. (Cl. 95-6) This invention relates to color photography and particularly to a method for preventing the formation of color fog or stain in photographic emulsions.

The method of color photography in which color-forming or coupler compounds combine with the development product of aromatic amino photographic developers to produce dyes is well known. The color formers or couplers may be added directly to the emulsion layers or may be incorporated in the developing solution as described in Fischer U. S. Patent 1,102,028, granted June 30, 1914, or they may be incorporated in a waterper'meable medium which is insoluble in the carrier for the sensitive silver salt as described in Marines and Godowsky U. S. Patent 2,304,940, December 15, 1942, and Jelley and Vittum U. S. Patent 2,322,027 granted June 15, 1943. Y

A difficulty frequently encountered in these processes is the formation of color f'og or stain. When the exposed material is developed in a color forming developer, dye fog is frequently formed in the emulsion layer. This is because the developing agent has been oxidized to some extent by the action of the air and the oxidized developer tends .to couple with the color-forming compound at places in the photographic material where no silver image is produced. It is well known that in these processes the dye should be formed only where the silver halide is -reduced to metallic silver, thereby oxidizing the developing agent to a form which couples with the color former. Once the developing agent is oxidized, it couples immediately with the color former whether a photographic image is present or not. 'Aerial oxidation of the developer or oxidation by means other than the photographic'image therefore converts the developer to a form which will immediately react with the color former to produce a color fog or stain. This effect is especially noticeable in materials having couplers incorporated in the sensitive emulsion layer since there is no coupler in the developing solution to react with any developing agent which is oxidized by the action of the air. Fog or stain arising from these causes is not readily controlled by the same procedures used to control silver fog.

The incorporation of various compounds in -photographic emulsions for controlling color fog or stain has been described in Weissberger and Vittum U. S. Patent 2,356,486, August 22, 1944, and Vittum and Wilder U. S. Patent 2,360,290, October 10,1944. However,

formation of colorfog or stain in photographicemulsions. A further object is to provide suitable non-diiiusing re- United States Patent-O the use of these simple reducing agents for preventing or ice ducing agents for incorporation in color photographic materials. A further object is to provide a color forming photographicemulsion having non-diffusing couplers and non-diffusing stain or fog inhibitors incorporated therein. Other objects will appearfr'om the following description of our invention.

These objects are accomplished by incorporating in a silver halide emulsion containing color couplers, as an inhibitor of color stain, a non-diffusing polymeric compound having as part ofits molecule recurring units containing two 'or more 'hydroxyl groups, two of which groups are part of the structure:

OH- OH 3=' oH-on= ;.-1( 3- where n is an integer from 1 to 2.

Compounds having this structure include polyvinyl polymers comprising units such as the following: 1 -'cHr-cn- 0111+ on OH -OH HO HO Vinyl hydroquinonemethacrylic acid interpolymer 4 CH2-CH CH- coon dooH H 1 Vinyl hydroouinonemalelc acid inter-polymer 5 -GHCHCH -QH- "Vinyl bydroqiiii1one-pqne'thyl styrene inter-polymer- "vin y i byerif innbile:sa-uniretn i styrene nitrpoiimer' Vinyl hydroquinonevinyl naphthalene interpolymer 9 CH2CHCH2CH c o 0.11. -on

Vinyl hydroquinonebutyl acrylate interpolymer COOClHO OH Vinyl hydroquinonebutyl methacrylate interpolymer CH:-CHCH2CH CHa- Vinyl methyl hydroquinonestyrene interpolymer CH:-(|JH-CHz(|3H-- Polyvinyl gentisal CHr-CHGH-CH I H OH Gentisylaminostyrenemaleic acid interpolymet -CH;CH OH 0H 0H Polyacrylylascorbic acid 0 -1 CH: CHsC ONH-Y-NH-C 0 OH H OH where Y is the group CH2CH2 or -CH2CH2 OCHzCHz :0CH2CH2- herewith by L. M. Minsk, D. D. Reynolds and J. L. R. Williams.

EXAMPLE 1 Polyvinyl gentisal Fifty-five and five-tenths grams of aqueous polyvinyl alcohol gel (17.28% solids) and 40.5 cc. of distilled water were heated on a steam bath with mechanical stirring in a three-necked flask equipped with stirrer, reflux condenser, and an inlet for dry nitrogen. Dry nitrogen was passed over the reaction mixture. When a smooth dope was obtained, 3 grams of gentisaldehyde followed by a solution of 12 cc. of concentrated hydrochloric acid diluted to cc. with distilled water, were added. Precipitation of a cake occurred. Heating and stirring under nitrogen was continued for 4 hours during which time redoping occurred to yield a smooth dope. The dope was poured in a fine stream into 3 liters of absolute ethyl alcohol, and the fibrous precipitate was extracted with ethyl alcohol in a Soxhlet extractor for 44 hours. The product was dried in a vacuum desiccator under constant water pump vacuum. Yield, 7 grams.

EXAMPLE 2 Polyacrylyl ascorbic acid Eight grams of polyacrylic anhydride were suspended in 100 ml. of dry pyridine. To this was added 0.86 cc. of distilled water, and the reaction mixture was refluxed for 20 minutes. Four grams of ascorbic acid were added and refluxing was continued for 30 minutes. A smooth dope, only slightly discolored, was obtained. Five cc. of distilled water were added and refluxing continued for another 3 minutes. The dope was poured into 1 liter of t-butyl alcohol and the precipitate obtained washed with fresh t-butyl alcohol. The product was given three reprecipitations from pyridine (100 cc.) into t-butyl alcohol (1 liter), with additional washing with fresh t-butyl alcohol on the suction funnel after each precipitation. After the last precipitation, washing and filtering as dry as possible on the funnel, the solid was dispersed in 100 cc. of distilled water. The air above the dope was displaced by nitrogen, and the sample was stored in an ice chest until used.

EXAMPLE 3 Gentisylaminostyrene-maleic acid interpolymer 1. Reaction of gentisaldehyde and aminostyrenemaleic acid interpolymer to form the anil. Ten grams of aminostyrene hydrochloride-maleic acid interpolymer were dispersed in 100 cc. of distilled water. To this dope were added with stirring 5.1 grams of gentisaldehyde. The reaction mixture which turned red almost immediately was left at room temperature for forty-five minutes with occasional stirring. It was then poured into one liter of acetone and the soft, gummy, red mass obtained was leached in fresh acetone until it became friable. The

product was ground in a mortar with fresh acetone, fur

EXAMPLE 4 Salt of ethylene diamine and 2,5-dihydrxy-p-benzene diacetic acid To a stirred solution of 9.0 g. (0.025 mole) of 2,5-dihydroxy-p-benzene diacetic acid in 400 cc. of absolute ethanol there was added slowly with stirring 2.6 g. (0.044 mole) of ethylene diamine dissolved in 200 cc. of absolute ethanol. The reaction mixture was then heated at 50 for one hour, cooled, and the salt filtered with suction. After drying at 60 in vacuo, it melted at 203 to 204. The yield was almost quantitative.

Polyamide from the salt of ethylene diamine and 2,5dihydraxy-p-benzenediacetic acid One gram of the salt of 2,5-dihydroxy-p-benzenediacetic acid with ethylene diamine was heated in a 20-mm. Pyrex test tube at 0.3 mm. at 190 to 195 until most of the white salt had fused hour). The reaction tube was cooled, the solid ground up, and extracted with water, and finally with alcohol. The purified solid was then dried in vacuo. Polyamides prepared in this manner at temperatures from 190-220 with reaction times from to 2 hours were insoluble in water, alcohol, and acetone, but soluble in dilute alkali.

EXAMPLE 5 Salt of ethylene glycol bisQS-aminoethyl) ether and 2,5-dihyar0xy-p-benzenediacetic acid A solution of 13.0 g. (0.08 mole) of ethylene glycol bis (B-aminoethyl) ether and 300 cc. of absolute ethanol was added with stirring to a solution of 18.3 g. (0.081 mole) of 2,S-dihydroxy-p-benzenediacetic acid in 500 cc. of absolute alcohol and the mixture allowed to stand at 50 for one hour. salt filtered and dried in vacuo at 60, M. P. 217-218". The yield was 21 g. of salt (68 per cent yield). Additional salt was obtained from the mother liquors by evaporation.

Polyamide from the salt of ethylene glycol bis (fl-aminoethyl) ether and 2,5-dihya'r0xy-p-benzenediacetic acid Seven grams of the salt was heated in a 30-min. Pyrex tube at 195210 and 0.3 to 0.5 mm. for 1 hour, at which time all of the salt had become molten. The reaction mixture was cooled, extracted with water, and then dissolved in 30 cc. of 60 per cent acetone and water. The polyamide was reprecipitated in water and dried in vacuo at room temperature over P205. The polymer thus obtained was soluble in 60 per cent acetone in water, insoluble in water, alcohol, and dioxane. It dissolved in dilute alkali and its solutions in 60 per cent acetone in water reduced ammoniacal silver nitrate.

The non-diffusing stain inhibitors of our invention can be incorporated directly in a gelatin emulsion containing couplers such as the emulsions described in Fischer U. S. Patent 1,102,028 or they may be incorporated in a water permeable medium which is insoluble in the carrier for the sensitive silver salt along with the insoluble coupler as described in Mannes and Godowsky U. S. Patent 2,304,940, and Jelley and Vittum U. S. Patent 2,322,027. They are useful in sensitive photographic elements having layers containing a coupler or couplers capable of producing dyes of a single color or in an emulsion layer containing a mixture of sensitive particles capable of pro- The reaction mixture was cooled, the

- cc. of 5% Alkanol B and 100 cc. of water.

ducing dyes of difierent colors. It will be noted that our polymeric stain inhibitors may be either water-soluble or oil-soluble, and therefore may be incorporated either directly in a gelatin emulsion, or first incorporated in a water-insoluble solvent. Water solubility is preferably, but not necessarily obtained by the presence of the saltforming -COOH groups included in the molecule; bases other than sodium hydroxide or other caustic alkali, for example, sodium carbonate or bicarbonate, may be used to effect solution. Oil solubility is enhanced by having in the molecule, alkyl, aryl or ester groups.

The incorporation of our non-diffusing reducing agents in a sensitive emulsion is described in the following examples:

EXAMPLE 6 Polyvinyl hydroquinone 2.56 g. of the magenta coupler 1-[4(2"-sulfobenzamido)phenyl]-3-stearamido-5-pyrazolone was dissolved in a mixture of 12 cc. of ethanol and 6 cc. of 20% aqueous sodium hydroxide. The solution was diluted with cc. of water and 2.5% citric acid solution added to bring the pH of the solution to 6.5, after which the volume of the neutralized solution was brought to 200 cc. To this solution was then added a solution of 0.16 g. of the antistain agent polyvinyl hydroquinone in 16 cc. of 50% ethanol. The resulting solution Was mixed with 200 cc. of a melted silver halide gelatin emulsion and coated. This coating showed markedly lower stain densities than were obtained with a similar coating without the antistain agent.

EXAMPLE 7 Copolymer 0 vinyl hydroquinone and methacrylic acid A solution of 4.3 grams of the coupler 1-phenyl-3- {3'-[2"-(2", 4"'-diarnylphenoxy) 5" (2""-sulfobenzamido)benzamidolbenzamido}-5-pyrazolone in 15 cc. of 20% NaOH was diluted with 200 cc. of water and neutralized to pH 6.8 by the addition of a 5% citric acid solution. The resulting coupler solution was mixed with 250 ml. of a melted sensitive AgBr gelatin emulsion, and to this mixture was added a solution of 0.3 gram of the polymeric anti-stain agent in 40 cc. of 50% ethanol. The mixture was then coated upon an opaque support consisting of pigmented cellulose ester. After drying, the coating was exposed and color processed to produce a magenta dye image. The magenta stain in the unexposed areas was markedly lower than that in a similar coating prepared without the addition of the polymeric anti-stain agent.

. acetaminobenzenesulfonyl) N('y-phenylpropyl)p toluidine and 0.2 gram of the polymeric anti-stain agent was dissolved in 15 cc. of di-n-butylphthalate by heating to C. The hot solution was poured with stirring into a solution prepared by mixing 60 cc. of 10% gelatin, 25 The hot mixture was then passed several times through a colloid mill to obtain a uniform fine dispersion which was mixed with 150 cc. of a melted sensitive AgBr gelatin emulsion and coated on a transparent film support. After drying and exposure, color processing produced a bright yellow dye image which had distinctly lower yellow stain in the unexposed areas than was obtained with a similar coating from which the polymeric anti-stain agent was omitted.

EXAMPLE 9 Copolymer of vinyl hydroquinone and 3,4-dimelhyl styrene A solution was prepared by heating to C. a mixture of 6 grams of the coupler 3-(benzoylacetamino)3- (4-tert-amylphenoxy) benzanilide, 0.6 gram of the polymeric anti-stain agent and 15 cc. of quinitol di-Z-ethylhexoate. The hot solution was poured with stirring into 150 cc. of an aqueous solution containing 8 grams of gelatin and 0.8 gram of Alkanol B. The mixture was passed several times through a colloid mill and then added to 140 cc. of a melted sensitive AgBr gelatin emulsion. The resulting mixture was coated on a paper support and dried. There was obtained after exposure and color processing a bright yellow dye image with distinctly lower yellow stain in the unexposed areas than was obtained with a similar coating from which the polymerit: anti-stain agent was omitted.

EXAMPLE 10 Copolymer of vinyl hydroquinone and butyl methacrylate A solution of 4.6 grams of the coupler Z-(diamylphenoxyacetamino)-4,6-dichloro-S-methylphenol and 0.65 gram of the polymeric anti-stain agent in 10 cc. of di-nbutylphthalate was prepared by heating a mixture of the components to 150 C. The hot solution was poured with stirring into 160 cc. of an aqueous solution of 5.5 grams of gelatin and 0.7 gram of Alkanol B. The resulting mixture was recycled through a colloid mill for five minutes, and the resulting fine dispersion was mixed v with 140 cc. of a melted sensitive AgBr gelatin emulsion.

The mixture was then coated on a transparent film support and dried. Color processing after exposure produced a clear cyan dye image in which the unexposed highlight areas were free from cyan stain.

EXAMPLE 11 Copolymer 2-methyl-5-vinyl hydraquinone and styrene A mixture of 5.2 grams of the coupler 1-(2',4,6-trichlorophenyl) 3 amido)benzamidol-S-pyrazolone and 1.2 grams of the polymeric anti-stain agent was dissolved in 18.2 cc. of tri-cresylphosphate by heating to 140 C. The hot solution was poured with stirring into 150 cc. of an aqueous solution containing 6 grams of gelatin and 1.0 gram of Duponal. The whole mixture was then passed several times through a colloid mill and then mixed with 180 cc. of a melted sensitive AgBr gelatin emulsion. The mixture was coated on a paper support and dried. After exposure, color development produced a bright magenta dye image with low magenta stain in the unexposed areas.

EXAMPLE 12 Polyvinyl gentisal A mixture of grams of the coupler l-hydroxy-2- [a-(2,4-diamylphenoxy)-n-butyl]-naphthamide and 0.5 gram of the polymeric anti-stain agent was dissolved in 30 cc. of tri-cresylphosphate by heating to 140 C. The hot solution was poured with stirring into a solution prepared by mixing 115 cc. of 10% gelatin, 35 cc. of 5% Alkanol B and 200 cc. of water. The whole mixture was then passed several times through a colloid mill. The resulting fine dispersion was mixed with 315 cc. of a melted sensitive AgBr gelatin emulsion and coated. After drying and exposure, color processing produced an intense cyan dye image in which the unexposed areas had markedly lower cyan stain than was obtained with a similar coating which did not contain the polymeric antistain agent. Fading tests on the two cyan dye images showed that the dye stability was not impaired by the presence of the anti-stain agent.

EXAMPLE l3 Condensation product of gentisaldehyde and the copolymer of amino styrene and maleic acid 3.2 grams of the coupler l-[4'-(2-sulfobenzamido)- phenyl]-3-stearamidmS-pyrazolone was dissolved in a mixture of 15 cc. of ethyl alcohol and 7.5 cc. of NaOH. The resulting solution was diluted with 200 cc. of water and the pH adjusted to 6.5 by the addition of 5% citric acid solution. This solution was then mixed with 250 cc. of a melted sensitive AgBr gelatin emulsion and to this mixture was added a solution of 0.5 gram of the polymeric anti-stain agent in cc. of water. The resulting mixture was coated on a transparent film support and dried. Color processing after exposure produced a clear magenta dye image in which the highlight areas were free from magenta stain, while a corresponding coating containing no anti-stain agent gave high magenta stain in the unexposed areas.

EXAMPLE 14 Polyamide from ethylene glycol bis-(fl-amirzoethyl) ether and 2,5-dihydr0xy-p-benzene diacetic acid 20 grams of the coupler 1-phenyl-3-{3'-[2"-(2"',4'- di-tert. amylphenoxy)-5"-(3", 5"-dicarbornethoxyphenylcarbamylvaleramido) benzamido]-benzamido}-5- pyrazolone was dissolved in a mixture of cc. of ethyl alcohol and 45 cc. of 25% NaOH. This solution was diluted to 600 cc. and the pH adjusted to 6.5 by the addition of a 5% citric acid solution. The neutralized coupler solution was then mixed with 1 kg. of a melted sensitive AgBr gelatin emulsion. To this mixture was then added a solution of 4 grams of the polymeric anti-stain agent in 200 cc. of 50% ethanol. The resulting mixture was coated on a transparent cellulose ester support and dried. On exposure and color processing, a clear magenta dye image was obtained in which the unexposed areas were free from magenta stain. A corresponding coating made without the anti-stain agent gave a considerably higher stain in the unexposed areas.

EXAMPLE 15 Condensation product of gentisaldehyde and the copolymat of aminostyrene and maleic acidc0upler in solvent dispersion Five grams of the coupler Z-(diamylphenoxyacetamino)-4,6-dichloro-S-methylphenol was dissolved in 15 grams of di-n-butylphthalate by heating to 150 C. The hot solution was poured with stirring into cc. of an aqueous solution of 5 grams of gelatin and 0.7 gram of Alkanol B. The resulting mixture was passed five times through a colloid mill, then mixed with 50 cc. of an aqueous solution containing 0.51 gram of the polymeric anti-stain agent, and the whole mixed thoroughly with cc. of a melted silver bromide gelatin emulsion. The mixture was coated on a white pigmented cellulose acetate support and dried. Color processing after exposure produced a bright cyan image with much lower cyan dye slain in the unexposed areas than in a similar coating containing no anti-stain agent.

Our compounds are employed in amounts of from 0.5% to 20% of the amount of coupler used in the emulsion although more or less of the non-diffusing stain inhibitors may be employed.

Vehicles other than gelatin may be used in our emulsions, e. g., polyvinyl alcohol, casein and its derivatives, gelatin derivatives, water-permeable cellulose derivatives, polyacrylamides and polyvinyl acetals, or mixtures of these with gelatin.

Our agents can be used in single layer or multi-laycr emulsion coatings or in mixed grain systems of the type described in Mannes and Godowsky U. S. Patent 2,388,859 and Fierke and Chechak U. S. Patent 2,490,749.

Our stain inhibitors are particularly useful with paper materials where it is important to reduce the minimum or fog densities. This applied both to negative developing paper and to reversal paper. Our stain inhibitors may, of course, also be used with transparency materials.

It will be understood that the examples and modifications disclosed herein are exemplary only and that our invention is to be taken as limited only by the scope of the appended claims.

What we claim is:

1. A color-forming photographic emulsion having reduced fogging tendency, comprising a silver halide emulsion having incorporated therein a non-diifusing color coupler and, as an inhibitor of color stain, a non-diffusing polymeric compound having as part of its molecule recurring units containing at least two hydroxyl groups, two of which hydroxyl groups are part of the structure:

OH OH =(OHOH=), (gwhere n is an integer from 1 to 2.

2. A color-forming photographic emulsion having reduced fogging tendency, comprising a silver halide emulsion having incorporated therein a non-difiusing color coupler and, as an inhibitor of color stain, a non-diffusing polymeric compound comprising a polymeric hydrocarbon chain having attached thereto recurring units containing two or more hydroxyl groups, two of which groups are part of the structure:

OH OH JJ=(HOH= g* whene n is an integer from 1 to 2.

3. A color-forming photographic emulsion having reduced fogging tendency, comprising a silver halide emulsion having incorporated therein a non-diffusing color coupler and as an inhibitor of color stain, a non-dilfusing polyvinyl hydroquinone.

4. A color-forming photographic emulsion having reduced fogging tendency, comprising a silver halide emulsion having incorporated therein a non-difiusing color coupler and as an inhibitor of color stain, a non-diffusing copolymer of vinyl hydroquinone and styrene.

5. A color-forming photographic emulsion having reduced fogging tendency, comprising a silver halide emulsion having incorporated therein a non-diffusing color coupler and as an inhibitor of color stain, a non-diffusing polyvinyl gentisal.

6. A color-forming photographic emulsion having reduced fogging tendency, comprising a silver halide emulsion having incorporated therein a non-diifusing color coupler and as an inhibitor of color stain, a non-diffusing polyacrylyl ascorbic acid.

7. The method of preventing formation of color fog in a photographic silver halide emulsion upon development of said emulsion by a color-forming development step, comprising subjecting said emulsion to color-forming development in the presence in said emulsion of a polymeric compound having as part of its molecule recurring units containing at least two hydroxyl groups, two of which hydroxyl groups are part of the structure:

a photographic silver halide emulsion upon development of said emulsion by a color-forming development step,

comprising subjecting said emulsion to color-forming development in the presence in said emulsion of a polymeric hydroquinone.

9. The method of preventing formation of color fog in a photographic silver halide emulsion upon development of said emulsion by a color-forming development step, comprising subjecting said emulsion to color-forming development in the presence in said emulsion of polyvinyl hydroquinone.

10. The method of preventing formation of color fog in a photographic silver halide emulsion upon development of said emulsion by a color-forming development step, comprising subjecting said emulsion to color-forming development in the presence in said emulsion of a copolymer of vinyl hydroquinone and styrene.

11. The method of preventing formation of color fog in a photographic silver halide emulsion upon development of said emulsion by a color-forming development step, comprising subjecting said emulsion to color-forming development in the presence in said emulsion of polyvinyl gentisal.

12. The method of preventing formation of color fog in a photographic silver halide emulsion upon development of said emulsion by a color-forming development step, comprising subjecting said emulsion to color-forming development in the presence in said emulsion of polyacrylyl ascorbic acid.

13. A color-forming photographic emulsion having reduced fogging tendency, comprising a silver halide emu1- sion having incorporated therein a non-diffusing color coupler and as an inhibitor of color stain, a non-diffusing polymer containing hydroquinone units.

14. A color-forming photographic emulsion having reduced fogging tendency, comprising a silver halide emulsion having incorporated therein a non-difiusing color coupler and as an inhibitor of color stain, a non-diffusing interpolymer of vinyl hydroquinone and another polymerizable compound.

15. The method of preventing formation of color fog in a photographic silver halide emulsion upon development of said emulsion by a color-forming development step, comprising subjecting said emulsion to color-forming development in the presence in said emulsion of a nondifiusing polymer containing hydroquinone units.

16. The method of preventing formation of color fog in a photographic silver halide emulsion upon development of said emulsion by a color-forming development step,

' comprising subjecting said emulsion to color-forming development in the presence in said emulsion of a non-diffusing interpolymer of vinyl hydroquinone and another polymerizable compound.

17. The method of preventing formation of color fog in a photographic silver halide emulsion upon development of said emulsion by a color-forming development step, comprising subjecting said emulsion to color-forming development in the presence in said emulsion of a non-difiusing polyamide derived from the salt of 2,5-dihydroxy-pbenzenediacetic acid and a diamine.

References Cited in the file of this patent UNITED STATES PATENTS 2,268,630 Wilmanns et al. Jan. 6, 1942 2,360,290 Vittum et al. Oct. 10, 1944 2,418,613 Allen et al. Apr. 8, 1947 

1. A COLOR-FORMING PHOTOGRAPHIC EMULSION HAVING REDUCED FOGGING TENDENCY, COMPRISING A SILVER HALIDE EMULSION HAVING INCROPORATED THEREIN A NON-DIFFUSING COLOR COUPLER AND, AS AN INHIBITOR OF COLOR STAIN, A NON-DIFFUSING POLYMERIC COMPOUND HAVING AS PART OF ITS MOLECULE RECURRING UNITS CONTAINING AT LEAST TWO HYDROXYL GROUPS, TWO OF WHICH HYDROXYL GROUPS ARE PART OF THE STRUCTURE: 